Trinucleotide cassettes increase diversity of T7 phage-displayed peptide library

Background  

Amino acid sequence diversity is introduced into a phage-displayed peptide library by randomizing library oligonucleotide DNA. We recently evaluated the diversity of peptide libraries displayed on T7 lytic phage and M13 filamentous phage and showed that T7 phage can display a more diverse amino acid sequence repertoire due to differing processes of viral morphogenesis.     

Letter to the editor: Electron diffraction for hydrated crystalline biopolymers: nigeran.

A method is presented to record electron diffraction diagrams on hydrated crystalline biopolymers. It involves quick-freezing of the hydrated crystals, which are maintained at a low temperature throughout the experiment. The technique is illustrated with lamellar single crystals of the linear polysaccharide nigeran. Water of hydration is shown to be in a sheet-like array and its removal is accompanied by development of lateral cracks. This morphological shrinkage coincides with an observed shortening of the b lattice parameter, which is normal to the lateral cracks.     

X-Ray and stereochemical studies on xylan diacetate

By means of x-ray fiber diffraction, it has been found that xylan diacetate crystallizes with two chains or four residues in a monoclinic cell (space group P2₁): a = 7.64, b = 12.44, c (fiber axis) = 10.31 Å, and γ = 85°. Pairs of residues are related by a twofold screw axis in the c direction. Based on the observed fiber repeat and chain symmetry, the probable conformation of a pair of xylose diacetate residues joined via a β-1,4′ linkage has been obtained by energy minimization methods. The conformations corresponding to a threefold screw axis and a twofold screw axis along the chain have been compared and the reason why xylan diacetate assumes a twofold screw axis seems to be due to intermolecular packing effects rather than intramolecular non-bonded interactions.     

Effect of nitrogen limitation on long-side-chain poly-beta-hydroxyalkanoate synthesis by Pseudomonas resinovorans.

Pseudomonas resinovorans produced poly-beta-hydroxyalkanoates (PHAs) when grown on hydrocarbons but not on glucose. In a chemostat culture, the PHA composition was beta-hydroxybutyrate (C4)-beta-hydroxyhexanoate (C6)-beta-hydroxyoctanoate (C8)-beta-hydroxydecanoate (C10) (1:15:75:9) on octanoate and C4-C6-C8-C10 (8:62:23:7) on hexanoic acid. Contrary to the reported behavior of Pseudomonas oleovorans, the PHA accumulation rate increased under ammonium limitation on octanoate.     

Mobility of lipid in complexes of amylose–fatty acids by deuterium and C solid state NMR

Palmitic and lauric acid complexes with amylose were studied by solid state methods: ¹³C CP/MAS NMR, deuterium NMR, X-ray powder diffraction and differential scanning calorimetry (DSC). The crystalline amylose complexes were found to be in a V-type sixfold single chain helix. The melting points of the complexes were over 100°C, at least 40–50°C higher than the melting points of the free fatty acids. CP/MAS ¹³C NMR spectra revealed two resonance peaks at 33.6 and 32.4 ppm for the palmitic acid, which were assigned as free and complexed fatty acid, respectively. A single resonance peak at 32.4 ppm was found for the lauric acid and assigned to the complex. The chemical shift of 32.4 ppm for the complexed fatty acids suggests a combined trans and gauche conformation for the fatty acid chain in the complex. T₁ relaxation measurements on the two palmitic acid resonances show different behavior: a very slow relaxation for the 33.6 ppm and a much faster relaxation (1.2 s) for the 32.4 ppm resonances. The latter was similar to the relaxation of the single resonance of the lauric acid (1.1 s). Temperature dependent deuterium spectra of the amylose–lauric acid and amylose–palmitic acid complexes suggest a complete complexation for the amylose–lauric acid, whereas the amylose–palmitic acid complex is partially disassociated by the thermal treatment. Based on the overall data, a partially disordered model is proposed: an imperfect helix with the fatty acid partly inside and partly out, depending on crystallization conditions and the necessity of placing the carboxyl head outside the V-helix.     

Malaria prophylaxis policy for travellers from Europe to the Indian Sub Continent

Background

Thick blood films are routinely used to diagnose Plasmodium falciparum malaria. Here, they were used to diagnose volunteers exposed to experimental malaria challenge.

Methods

The frequency with which blood films were positive at given parasite densities measured by PCR were analysed. The poisson distribution was used to calculate the theoretical likelihood of diagnosis. Further in vitro studies used serial dilutions to prepare thick films from malaria cultures at known parasitaemia.

Results

Even in expert hands, thick blood films were considerably less sensitive than might have been expected from the parasite numbers measured by quantitative PCR. In vitro work showed that thick films prepared from malaria cultures at known parasitaemia consistently underestimated parasite densities.

Conclusion

It appears large numbers of parasites are lost during staining. This limits their sensitivity, and leads to erroneous estimates of parasite density.     

Far ultraviolet optical activity of saccharide derivatives. I. Xylan and cellulose acetates

Optial rotatory dispersion (ORD) and Circular dichroism (CD) spectra of several β-1,4 xylan and cellulose acetates and some of their oligomers were investigated. The CD spectra proved considerably superior in terms of information content and interpretability. Comparison of the xylan and cellulose acetate series which also included partially substited cellulose acetates showed that the sign of the CD of the C(6) acetyl was negative. Likewise, the combined contribution of C(1) and C(4) to their equatorially substituted acetyls was positive (with C(1) definitely Positive) and the combined contribution of C(2)_eq and C(3)_eq negative. The solution conformations of both polysaccharide acetates appeared to be random. The CD of White birch xylan acetate which is substituted on the average at every tenth residue with a 4-O-methyl glucuronic acid substituent, was sensitive to it. The xylan oligomer series also illustrated that CD may be used to determine the degree of polymerization of these oligomers up to about 20.